Signal receiving device and signal receiving method

ABSTRACT

A signal receiving device and signal receiving method to pass a desired frequency component of an intermediate frequency signal by using an IF filter without increasing a chip area. The signal receiving device comprises: a mixer to mix a received frequency signal with a local oscillation frequency signal to generate an intermediate frequency signal; an IF filter to pass a predetermined frequency component of the intermediate frequency signal; a controlling part which adjusts, according to a frequency band of the intermediate frequency signal, the frequency band of the IF filter, and adjust, according to a center frequency set in the IF filter that fluctuates with the adjustment, a center frequency of the intermediate frequency signal to be inputted in the IF filter; and a demodulating part to demodulate a frequency component of the intermediate frequency signal outputted after passing through the IF filter.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a signal receiving device and signalreceiving method to generate and demodulate an IF (IntermediateFrequency) signal by combining a receiving RF (radio frequency) signaland a local oscillating signal.

2. Description of Related Art

Conventionally a signal receiving device is known wherein an IFfiltering circuit is equipped to receive an RF signal, and generate anIF signal of an intermediate frequency by mixing the RF signal and alocal oscillating signal so as to filter the IF signal. As an IFfiltering circuit, generally an active filter is used wherein aresistance and a condenser are set as a filter constant. A resistancevalue and a capacity value of a condenser are optimized according to aformat of an RF signal to receive, an IF frequency, a passing bandwidth,an out-of-band attenuation, or the like.

For example, in order to able to receive a plurality of RF signalshaving different bandwidths required with a signal receiving device, amethod is known wherein the signal receiving device is installed with aplurality of IF filtering circuits so as to select an optimal IFfiltering circuit for an RF signal to receive (Patent Literature 1).

Patent Literature 1: Japanese Patent Kokai No. 2002-217768 SUMMARY OFTHE INVENTION

However, there was a problem in that a chip area resulted in increasingif a signal receiving device was installed with a plurality of IFfiltering circuits similarly to the constitution as disclosed in PatentDocument 1 so as to adapt to a plurality of modulation rates ormodulation methods.

Moreover, generally, errors occur in a resistance value of resistance ora capacity value of a condenser comprising an IF filter caused byproduction variations, causing a design target value of a filterpassband different from an actual value. There was a problem in that ifthe filter passband was designed to be large in advance, a design targetvalue of the filter passband could be dealt with even if there wasdeviation, however, a noise was increased.

Moreover, according to a conventional signal receiving device, there wasa problem in that, if a filter passband was changed by adjusting onlyeither a resistance value or a capacity value that was to become afilter constant, a center frequency of an IF filter was changedsimultaneously so as to separate from an original IF frequency, therebyan optimal filter passband could not be always set.

The present invention has been made in light of the above-mentionedproblems, and an object thereof is to provide a signal receiving deviceand signal receiving method to pass a desired frequency component of anintermediate frequency signal by using an IF filter without increasing achip area.

According to the present invention, a signal receiving device comprises:a mixer to mix a received frequency signal with a local oscillationfrequency signal generated by a local oscillator so as to generate anintermediate frequency signal; an IF filter in which a center frequencyof a passable frequency signal and a frequency band are set so as topass a predetermined frequency component of the intermediate frequencysignal; a controlling part which adjusts, according to a frequency bandof the intermediate frequency signal, the frequency band set in the IFfilter, and adjusts, according to a center frequency set in the IFfilter that fluctuates with the adjustment, a center frequency of theintermediate frequency signal to be inputted in the IF filter; and ademodulating part to demodulate a frequency component of theintermediate frequency signal outputted after it passes through the IFfilter.

Moreover, according to the present invention, a signal receiving methodcomprises: a mixer step to mix a frequency signal received with a localoscillation frequency signal generated by a local oscillator so as togenerate an intermediate frequency signal; a filter step to pass apredetermined frequency component of the intermediate frequency signalby an IF filter in which a center frequency of a passable frequencysignal and a frequency band are set; a first adjusting step to adjust afrequency band set in the IF filter according to the frequency band ofthe intermediate frequency signal; a second adjusting step to adjust acenter frequency of the intermediate frequency signal in response to afluctuation of the center frequency set in the IF filter caused byadjustment of a frequency band set in the IF filter; and a demodulatingstep to demodulate the intermediate frequency signal that has passedthrough the IF filter.

According to the signal receiving device and signal receiving method ofthe present invention, it is possible to use an IF filter so as to passa desired frequency component of an intermediate frequency signalwithout increasing a chip area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a constitution of a signalreceiving device that is an embodiment of the present invention;

FIG. 2 is a block diagram illustrating a constitution of the IF filterof FIG. 1;

FIG. 3 is a circuit diagram illustrating a constitution of a condenserblock included in the high-pass filter of FIG. 2;

FIG. 4 is a circuit diagram illustrating a constitution of a condenserblock included in the low-pass filter of FIG. 2;

FIG. 5 is a flow chart illustrating a routine of an output adjustingprocessing of an IF filter;

FIG. 6 is a block diagram illustrating a constitution of a controllingcircuit and a condenser block.

DETAILED DESCRIPTION OF THE INVENTION

Below, the embodiments of the present invention will be described indetail by referencing the drawings.

First Embodiment

FIG. 1 is a block diagram illustrating a constitution of a signalreceiving device 1 that is an embodiment of the present invention.

The signal receiving device 1 comprises: a mixer 13 to mix a receivedfrequency signal with a local oscillation frequency signal generated bya local oscillator 12 so as to generate an intermediate frequencysignal; an IF filter 14 in which a center frequency of a passablefrequency signal and a frequency band are set so as to pass apredetermined frequency component of the intermediate frequency signal;a controlling part 17 in which, according to a frequency band of theintermediate frequency signal, the frequency band set in the IF filter14 is adjusted, and according to a center frequency set in the IF filter14 that fluctuates with the adjustment, a center frequency of theintermediate frequency signal to be inputted in the IF filter 14 areadjusted; and a demodulating part 16 to demodulate a frequency componentof the intermediate frequency signal outputted after it passes throughthe IF filter 14.

A filter adjusting input signal (hereafter also referred to as a firstcontrolling input signal) is inputted in the IF filter 14. Anoscillating frequency setting input signal (hereafter also referred toas a second controlling input signal) is inputted in the localoscillator 12.

A receiving part 10 receives an RF signal wirelessly and supplies it toan amplifier 11.

The amplifier 11 is an amplifier such as a low-noise amplifier (LNA),for example, to amplify the RF signal.

The local oscillator 12 is a local oscillator to generate a localoscillating signal. A frequency of the local oscillating signal is seton the basis of an oscillating frequency setting input signal suppliedexternally. If the local oscillator 12 is a PLL (Phase Locked Loop)local oscillator, the oscillating frequency setting input signal is asignal to indicate a division ratio. In this case, the local oscillator12 sets a frequency of the local oscillating signal on the basis of aninput reference signal supplied from a crystal oscillator (notillustrated) and the division ratio indicated by the oscillatingfrequency setting input signal. The PLL local oscillator may have ageneral constitution including a VCO (Voltage Controlled Oscillator),loop filter, phase comparator, or frequency divider (all of which notillustrated). The frequency divider supplies a division signal generatedon the basis of the division ratio indicated by the oscillatingfrequency setting input signal to the phase comparator.

The mixer 13 is a mixer to mix an RF signal amplified by the amplifier11 with a local oscillating signal generated by the local oscillator 12so as to generate an intermediate frequency signal, that is to say an IFsignal.

The IF filtering circuit (hereafter referred to as an IF filter) 14passes only a frequency component of a predetermined band of a frequencycomponent in the IF signal. A filter characteristic of the IF filter 14is set by a filter adjusting input signal supplied externally. Thefilter characteristic is a characteristic to decide a passing frequencyprofile.

An amplifier 15 is an amplifier to amplify an output signal of the IFfilter 14 within a predetermined amplitude constraint.

A demodulator 16 demodulates a signal amplified by the amplifier 15 soas to output a base band signal.

The controlling part 17 adjusts a frequency band set in the IF filter 14according to a frequency bandwidth of an output signal of the IF filter14. Moreover, the controlling part 17 adjusts a center frequency of anintermediate frequency signal inputted into the IF filter 14 accordingto a center frequency of an output signal of the IF filter 14 thatfluctuates by the adjustment of the frequency bandwidth. Morespecifically, the controlling part 17 adjusts a center frequency of anintermediate frequency signal by inputting an oscillating frequencysetting input signal in the local oscillator 12 so as to fluctuate afrequency of a local oscillating signal.

For example, the controlling part 17 may operate according to a signalfrom an information processing part (not illustrated) such as a CPU, ora signal or the like manually set by an operator. The controlling part17 may be divided into two portions wherein one portion adjusts afrequency band set in the IF filter 14, while other portion adjusts acenter frequency of an intermediate frequency signal.

The filter adjusting input signal and oscillating frequency settinginput signal described above are signals manually input that areobtained by using an electronic component having a manually variablecharacteristic, for example. These signals may be generated by thecontrolling circuit. When a controlling input signal is automaticallygenerated, it is possible to obtain an optimal filtering characteristicand a local oscillation frequency to match it by associating contents ofthese signals to each other on the basis of a rule of thumb, forexample. In other words, if a filter adjusting input signal indicating acharacteristic thereof is inputted, a local oscillating signal having anoptimal frequency corresponding to the filter characteristic isgenerated.

FIG. 2 is a block diagram illustrating a constitution of an IF filter14. The IF filter 14 comprises a high-pass filter 20 and low-pass filter30. An IF signal from the mixer 13 is inputted into an inputtingterminal 21 of the high-pass filter 20. Output of the high-pass filter20 is inputted into the low-pass filter 30. Output of the low-passfilter 30 is supplied to the amplifier 15 from the outputting terminal31.

The high-pass filter 20 is a filter to pass a frequency component havinga predetermined frequency band or greater of a frequency component inthe IF signal. The high-pass filter 20 includes a condenser block 22 anda resistance 23. The condenser block 22 is connected between theinputting terminal 21 and a connecting terminal 25. The resistance 23 isconnected between the connecting terminal 25 and a grounding terminal26. Grounding potential is supplied to the grounding terminal 26. The IFsignal is inputted into the inputting terminal 21 and outputted from theconnecting terminal 25. A capacity value of the condenser block 22 canbe freely set on the basis of a content of a filter adjusting inputsignal inputted into a signal inputting part 24.

The low-pass filter 30 is a filter to pass a frequency component havinga predetermined frequency band or smaller of a frequency component inthe IF signal. The low-pass filter 30 includes a resistance 32 and acondenser block 33. The resistance 32 is connected between a connectingterminal 35 and outputting terminal 36. The condenser block 33 isconnected between the outputting terminal 36 and a grounding terminal37. Grounding potential is supplied to the grounding terminal 37. An IFsignal that passes through the high-pass filter 20 is inputted into theinputting terminal 35 and outputted from the connecting terminal 31. Acapacity value of the condenser block 33 can be freely set on the basisof a content of a filter adjusting input signal inputted into a signalinputting part 34.

FIG. 3 is a circuit diagram illustrating a constitution of a condenserblock 22 included in the high-pass filter 20.

A condenser CH0 is disposed between the inputting terminal 21 andconnecting terminal 25 via a switch SH0. Similarly, each of condensersCH1-CHn (n is an integer equal to or greater than 2) is disposed betweenthe inputting terminal 21 and connecting terminal 25 via one ofcorresponding switches SH1-SHn. The constitution causes the condensersCH0-CHn to be connected in parallel to each other.

The signal inputting part 24 comprises signal inputting terminalsTH0-THn. A filter adjusting input signal is inputted into the signalinputting terminals TH0-THn. A filter adjusting input signal is a signalindicating a binary bit string, for example. A bit value correspondingto one of a plurality of bit values comprising the bit string isinputted into each of the signal inputting terminals TH0-THn. If abinary bit string is “1 . . . 01” for example, bit value “1” is inputtedinto the signal inputting terminal TH0, bit value “0” is inputted intothe signal inputting terminal TH1, . . . , and bit value “1” is inputtedinto the signal inputting terminal THn respectively.

The switch SH0 turns on or off according to a bit value inputted intothe signal inputting terminal TH0. Similarly, each of the switchesSH1-SHn turns on or off according to a bit value inputted into thesignal inputting terminals TH1-THn.

Each of the switches SH0-SHn turns off if a bit value is “0” and turnson if a bit value is “1,” for example. By turning on or off the switchesSH0-SHn, some of the condensers CH0-CHn are selectively connected inparallel between the inputting terminal 21 and connecting terminal 25.Accordingly, it is possible to change a capacity value of the condenserblock 22, thereby optimizing the filter characteristic.

FIG. 4 is a circuit diagram illustrating a constitution of a condenserblock 33 included in the low-pass filter 30.

A condenser CL0 is disposed between the outputting terminal 36 andgrounding terminal 37 via a switch SL0. Similarly, each of condensersCL1-CLn (n is an integer equal to or greater than 2) is disposed betweenthe outputting terminal 36 and grounding terminal 37 via one ofcorresponding switches SL1-SLn. The constitution causes the condensersCL0-CLn to be connected in parallel to each other.

A signal inputting part 34 comprises signal inputting terminals TL0-TLn.A filter adjusting input signal is inputted into the signal inputtingterminals TL0-TLn. A filter adjusting input signal is a signalindicating a binary bit string, for example. A bit value correspondingto one of a plurality of bit values comprising the bit string isinputted into each of the signal inputting terminals TL0-TLn.

The switch SL0 turns on or off according to a bit value inputted intothe signal inputting terminal TL0. Similarly, each of the switchesSL1-SLn turns on or off according to a bit value inputted into thesignal inputting terminals TL1-TLn.

Each of the switches SL0-SLn turns off if a bit value is “0” and turnson if a bit value is “1,” for example. By turning on or off the switchesSL0-SLn, some of the condensers CL0-CLn are selectively connected inparallel between the outputting terminal 36 and grounding terminal 37.Accordingly, it is possible to change a capacity value of the condenserblock 33, thereby optimizing the filter characteristic.

Below, setting processing will be described wherein a signal having adesired frequency profile is outputted from the IF filter 14. Thesetting processing is performed in a characteristic inspection beforeproduct shipment, for example. The setting processing may be performedby a user after products are shipped or can be performed as needed. Thesetting processing may be performed according to a change of an assumedinputting frequency signal.

The receiving method of a frequency signal according to the presentinvention comprises: a mixer step to mix a frequency signal receivedwith a local oscillation frequency signal generated by a localoscillator 12 so as to generate an intermediate frequency signal; anfilter step to cause an IF filter 14 in which a center frequency of apassable frequency signal and a frequency band are set to pass apredetermined frequency component of the intermediate frequency signal;a first adjusting step to adjust a frequency band set in the IF filter14 according to the frequency band of the intermediate frequency signal;a second adjusting step to adjust a center frequency of the intermediatefrequency signal according to a fluctuation of the center frequency setin the IF filter 14 caused by adjustment of a frequency band set in theIF filter 14; and a demodulating step to demodulate the intermediatefrequency signal that passes through the IF filter 14.

As a premise, the signal receiving device 1 operates as follows. First,the receiving part 10 receives an RF signal. The amplifier 11 amplifiesthe RF signal. The local oscillator 12 generates a local oscillatingsignal. The mixer 13 mixes the amplified RF signal with the localoscillating signal so as to generate an intermediate frequency signal.The IF filter 14 passes only a frequency component in a predeterminedband of a frequency component in the intermediate frequency signal. Theamplifier 15 amplifies an output signal of the IF filter 14. Thedemodulator 16 demodulates a signal amplified by the amplifier 15.

A filter adjusting input signal has been inputted into the IF filter 14so as to initialize in a desired frequency band. According to a contentof the filter adjusting input signal, a capacity value of the condenserblock 22 of the high-pass filter 20 and a capacity value of thecondenser block 33 of the low-pass filter 30 comprising the IF filter 14are set. Accordingly, the filter characteristic of the IF filter 14 isinitialized.

A cut-off frequency fHPF of the high-pass filter 20 is defined by thefollowing expression (1).

$\begin{matrix}{f_{HPF} = \frac{1}{2\pi \; C_{S}R_{H}}} & (1)\end{matrix}$

A cut-off frequency fLPF of the low-pass filter 30 is defined by thefollowing expression (2).

$\begin{matrix}{f_{LPF} = \frac{1}{2\pi \; C_{S}R_{L}}} & (2)\end{matrix}$

According to the expressions (1) and (2), the bandwidth BW of the IFfilter 14 is expressed by the following expression (3).

$\begin{matrix}{{BW} = {\frac{1}{2\pi \; C_{S}}( {\frac{1}{R_{H}} - \frac{1}{R_{L}}} )}} & (3)\end{matrix}$

Furthermore, according to the expressions (1) and (2), the centerfrequency f_(center) is expressed by the following expression (4).

$\begin{matrix}{f_{center} = {\frac{1}{4\pi \; C_{S}}( {\frac{1}{R_{H}} + \frac{1}{R_{L}}} )}} & (4)\end{matrix}$

From the expression (3) and (4), it is understood that the bandwidth BWand center frequency f_(center) change inversely proportional to thecapacity value Cs of the condenser blocks 22, 33.

A capacity ratio of each of the condensers CH0-CHn comprising thecondenser block 22 is 2n, for example. That is to say, if a capacityvalue of the condenser CH0 is C0, a capacity value of the condenser CH1is 2×C0, a capacity value of the condenser CH2 is 4×C0, . . . , acapacity value of the condenser CHn is n×C0. In this case, the capacityvalue Cs of the condenser block 22 can be gradually changed in a rangeof C0 to (2^(n+)−1)×C0. It is the same with the condenser block 33.

As described above, by inputting a filter adjusting input signal, it ispossible to initialize a desired filter characteristic. Furthermore, thecenter frequency f_(center) can be initialized according to a filteradjusting input signal. A resistance value RH of the resistance 23 and aresistance value RL of the resistance 32 included in the IF filter 14,each capacity value of the condensers CH0-CHn, CL0-CLn included in thecondenser block 22, 33 may be any value according to a design conditionrespectively.

Thereafter, output of the IF filter 14 is subject to the adjustingprocessing. FIG. 5 is a flow chart illustrating a routine of an outputadjusting processing of an IF filter. Below, the output adjustingprocessing of an IF filter will be described by referencing FIG. 5.

First, the controlling part 17 adjusts the frequency bandwidth set inthe IF filter 14 (Step S1). The controlling part 17 decides an amount toadjust according to the content of a setting signal externally. Thesetting signal is a signal to set the capacity value Cs of the condenserblocks 22, 33. More specifically, the setting signal is a signalindicating a binary bit string consisting of “0” and “1” for example,inputted into the signal inputting terminals TH0-THn so as to turn on oroff each of the switches SH1-SHn of the condenser block 22, for example.Furthermore, a similar setting signal can be supplied into the signalinputting terminals TH0-THn so as to turn on or off the switches SL1-SLnof the condenser block 33. The amount to adjust by the controlling part17 is decided by changing the capacity value of condenser blocks 22, 33included in the IF filter 14. By this adjustment, a deviation in thefrequency bandwidth caused by production variations of the IF filter 14can be corrected, and further the frequency bandwidth can be set to theone corresponding to a desired inputting frequency signal. Below, thesignal receiving device is described wherein a frequency of a localoscillating signal is set to be lower than a frequency of an RF signal,that is to say, it is set as what is called a lower-side local.

For example, if an actual frequency bandwidth is narrower than a desiredfrequency bandwidth, a setting signal is sent to the controlling part 17so as to widen the frequency bandwidth. According to the content of thesetting signal, the controlling part 17 inputs a filter adjusting inputsignal into the IF filter 14 so as to decrease the capacity value Cs ofthe condenser blocks 22, 33. The filter adjusting input signal decreasesthe number of parallel connections of the condensers CH0-CHn in thehigh-pass filter 20 and the number of parallel connections of thecondensers CL0-CLn in the low-pass filter 30. A decrease in the capacityvalue Cs increases the center frequency of the IF filter 14.

Next, the controlling part 17 adjusts a center frequency of anintermediate frequency signal (Step S2). The controlling part 17 decidesan amount to adjust according to a content of a setting signalexternally. The amount to adjust is decided by a content of anoscillating frequency setting input signal to a local oscillator 12.

For example, a setting signal to widen the frequency bandwidth describedabove also includes a content to decrease the oscillation frequency.According to the content of the setting signal, the controlling part 17inputs an oscillating frequency setting input signal to decrease theoscillation frequency to the local oscillator 12, thereby increasing theIF frequency. If the local oscillator 12 is a PLL, the oscillatingfrequency setting input signal decreases an N value of the divisionratio 1/N.

Furthermore, for example, if an actual frequency bandwidth is wider thana desired frequency bandwidth, a setting instruction is sent to thecontrolling part 17 so as to narrow the frequency bandwidth. Accordingto the content of the setting signal, the controlling part 17 inputs afilter adjusting input signal into the IF filter 14 so as to increasethe capacity value Cs of the condenser blocks 22, 33. The filteradjusting input signal increases the number of parallel connections ofthe condensers CH0-CHn in the high-pass filter 20 and the number ofparallel connections of the condensers CL0-CLn in the low-pass filter30. By increasing the capacity value Cs, the center frequency of the IFfilter 14 decreases.

For example, a setting signal to narrow the frequency bandwidthdescribed above also includes a content to increase the oscillationfrequency. According to the content of the setting signal, thecontrolling part 17 inputs an oscillating frequency setting input signalto increase the center frequency of the oscillation frequency to thelocal oscillator 12, thereby decreasing the IF frequency. If the localoscillator 12 is a PLL, the oscillating frequency setting input signalincreases an N value of the division ratio 1/N.

The above example illustrates a case of a lower side local, however, inthe case of a signal receiving device 1 wherein a frequency of a localoscillating signal is higher than a frequency of an RF signal, that isto say, if it is set as what is called an upper side local, adjustmentof the controlling part 17 is performed as follows. If a setting signalincludes a content to widen a frequency bandwidth, a center frequency ofthe IF filter is increased by adjusting the frequency band. A settingsignal in this case also includes a content to increase the oscillationfrequency. According to the content of the setting signal, thecontrolling part 17 inputs an oscillating frequency setting input signalto increase the center frequency of the oscillation frequency to thelocal oscillator 12. If a setting signal includes a content to narrow afrequency bandwidth, a center frequency of the IF filter is decreased byadjusting the frequency band. A setting signal in this case alsoincludes a content to decrease the oscillation frequency. According tothe content of the setting signal, the controlling part 17 inputs anoscillating frequency setting input signal to decrease the centerfrequency of the oscillation frequency to the local oscillator 12.

By inputting a filter adjusting input signal and oscillating frequencysetting input signal having the content, a frequency profile of anoutput signal of the IF filter 14 can be optimally adjusted. Forexample, if the contents of a filter adjusting input signal andoscillating frequency setting input signal are fixed for the adjustmentbefore shipment, errors of the filter characteristic have been resolvedby the time the signal receiving device 1 is shipped.

As described above, according to the signal receiving device 1 of thisembodiment, the frequency band set in the IF filter depending on thecontent of a setting signal is adjusted, and a center frequency of theIF filter that fluctuates due to the adjustment is also adjusteddepending on the content of a setting signal. According to theconstitution, it is not necessary to provide a plurality of IF filtersas practiced by a conventional technology, which produces an effect inthat a chip area is small. Furthermore, by inputting a filter adjustinginput signal, the bandwidth BW can be changed, and the center frequencyf_(center) that fluctuates by the change can be adjusted by changing thecontent of an oscillating frequency setting input signal, thereby errorsof the IF filter characteristic caused by production variations can becompensated. Furthermore, it becomes possible to realize an optimal IFfilter characteristic according to various frequency signals inputted.

Second Embodiment

FIG. 6 is a block diagram illustrating a constitution of a controllingpart 17, a condenser block 22, and a condenser block 33. Theconstitutions of the signal receiving device 1 (FIG. 1) and IF filter 14(FIG. 2-FIG. 4) are similar to Those of First Embodiment.

The controlling part 17 comprises registers 51-1 to 51-m, a selector 52,registers 53-1 to 53-m, a selector 54, registers 55-1 to 55-m, aselector 56, and a controlling circuit 57.

Data indicating a content of an oscillating frequency setting inputsignal is memorized in each of the registers 51-1 to 51-m. Datadifferent from each other is memorized in each of the registers 51-1 to51-m. The data is supplied from the controlling circuit 57. If the localoscillator 12 is a PLL, the data indicates a division ratio.

The selector 52 selects one of the registers 51-1 to 51-m according to aselection instruction supplied from the controlling circuit 57, and thenoutputs an oscillating frequency setting input signal that has the datamemorized in one of the selected registers. The oscillating frequencysetting input signal is supplied to the local oscillator 12 illustratedin FIG. 1.

Data indicating a content of a filter adjusting input signal ismemorized in each of the registers 53-1 to 53-m. Data different fromeach other is memorized in each of the registers 53-1 to 53-m. The datais n-bit data to be supplied to the inputting terminals TH0-THn of thecondenser block 22. The data is supplied from the controlling circuit57.

The selector 54 selects one of the registers 53-1 to 53-m according to aselection instruction supplied from the controlling circuit 57, and thenoutputs a filter adjusting input signal that has the data memorized inone of the selected registers. The filter adjusting input signal issupplied to the inputting terminal TH0-THn of the condenser block 22.

Data indicating a content of a filter adjusting input signal ismemorized in each of the registers 55-1 to 55-m. Data different fromeach other is memorized in each of the registers 55-1 to 55-m. The datais n-bit data to be supplied to the inputting terminals TL0-TLn of thecondenser block 33. The data is supplied from the controlling circuit57.

The selector 56 selects one of the registers 55-1 to 55-m according to aselection instruction supplied from the controlling circuit 57, and thenoutputs a filter adjusting input signal that has the data memorized inone of the selected registers. The filter adjusting input signal issupplied to the inputting terminals TL0-TLn of the condenser block 33.

The controlling circuit 57 supplies data indicating a content of anoscillating frequency setting input signal to each of the registers 51-1to 51-m, and supplies data indicating a content of a filter adjustinginput signal to each of the registers 53-1 to 53-m and registers 55-1 to55-m. These data vary depending on each condition such as a modulationmethod, modulation rate, or the like. They are data setting anappropriate filter characteristic to match the condition and an IFfrequency corresponding to a center frequency that is adapted thereto.Data memorized by the registers 51-1 to 51-m is associated to each otherwith data memorized by the registers 53-1 to 53-m and registers 55-1 to55-m on the basis of thumb rules or the like, for example. Thecontrolling circuit 57 can be constituted as a microprocessor chip forLSI's or the like, for example.

For example, filter adjusting data is memorized in the register 51-1,and oscillation frequency setting data is memorized in the registers53-1, 55-1 so as to generate an IF frequency matching the filtercharacteristic that the data indicates. The controlling circuit 57supplies a selection instruction to select the register 51-1 dependingon a content of an external setting signal to the selector 52, andsupplies a selection instruction to select the registers 53-1, 55-1 tothe selectors 54, 56. When the controlling circuit 57 selects a filtercharacteristic, the constitution allows an appropriate center frequencycorresponding thereto to be selected.

As described above, the controlling circuit 55 supplies a selectionsignal to select one of the registers 51-1 to 51-m and registers 53-1 to53-m respectively to the selectors 52, 54, and 56 depending on a contentof an external setting signal.

Thus, according to the signal receiving device 1 of this embodiment, thefilter adjusting data is associated with the oscillation frequencysetting data to each other to be memorized in the register, a filtercharacteristic is selected depending on a condition such as a modulationmethod, modulation rate, or the like to be actually used, therebyselecting an IF frequency related thereto. When a filter characteristicis selected, the constitution allows an appropriate IF frequencycorresponding thereto to be selected.

First and second embodiments are examples to change the filtercharacteristic by varying a capacity value of the IF filter 14, however,the filter characteristic can be changed by making a resistance value ofthe IF filter 14 variable. In this case, the IF filter 14 is constitutedto include a capacity element and a resistance block that is connectedto the capacity element and a resistance value is switchable. The IFfilter 14 comprises a high-pass filter and low-pass filter, for example.Each of the high-pass filter and low-pass filter includes a capacityelement and a resistance block that is connected thereto and theresistance value is variable. The resistance block is constituted toinclude a plurality of resistances, for example, and some of theresistances are connected in parallel according to a setting signalsupplied from externally or a CPU (not illustrated), for example. Thesetting signal is a signal to turn on or off each switch connected inseries to each of the resistances. By causing the switch to turn on oroff so as to change the number of connected resistances in parallel, aresistance value of the resistance block can be changed. By changing aresistance value of the resistance block, the frequency band that is tobe set in the IF filter can be adjusted.

This application is based on Japanese patent application No. 2011-042151which is hereby incorporated by reference.

1. A frequency signal receiving device comprising: a mixer which mixes areceived frequency signal with a local oscillation frequency signalgenerated by a local oscillator so as to generate an intermediatefrequency signal; an IF filter in which a center frequency of a passablefrequency signal and a frequency band are set so as to pass apredetermined frequency component of the intermediate frequency signal;a controlling part which adjusts, according to a frequency band of theintermediate frequency signal, the frequency band set in the IF filter,and adjusts, according to a center frequency set in the IF filter thatfluctuates with the adjustment, a center frequency of the intermediatefrequency signal to be inputted in the IF filter; and a demodulatingpart which demodulates a frequency component of the intermediatefrequency signal outputted after it passes through the IF filter.
 2. Thefrequency signal receiving device according to claim 1, wherein thecontrolling part adjusts a center frequency of the intermediatefrequency signal by adjusting a center frequency of the localoscillation frequency signal.
 3. The frequency signal receiving deviceaccording to claim 1, wherein the IF filter comprises a resistance and acondenser block that is connected to the resistance and a capacitythereof is switchable; and a frequency band set in the IF filter isadjusted by adjusting a capacity value of the condenser block.
 4. Thefrequency signal receiving device according to claim 3, wherein thecondenser block comprises a plurality of condensers that are connectedin parallel to each other so that connection to the resistance can beselected; and a capacity value of the condenser block is adjusted byadjusting the number of the plurality of condensers to be connected tothe resistance.
 5. The frequency signal receiving device according toclaim 1, wherein the IF filter comprises a high-pass filter and alow-pass filter connected in series to each other.
 6. The frequencysignal receiving device according to claim 2, wherein a capacity valueof the condenser block is adjusted on the basis of first information ofa fist memory part in which the first information on the number of theplurality of condensers to be connected to the resistance is memorizedin advance, to be selected according to a frequency band of theintermediate frequency signal.
 7. The frequency signal receiving deviceaccording to claim 6, wherein the first memory part is equipped with aplurality of first registers equipped with the first information set foreach frequency band of the intermediate frequency signal that is assumedin advance; and a capacity value of the condenser block is adjusted onthe basis of the first information of the first register selectedaccording to a frequency band of the intermediate frequency inputted. 8.The frequency signal receiving device according to claim 1, wherein acenter frequency of the intermediate frequency signal is adjusted basedon second information of a second memory part in which memorized inadvance is the second information on the center frequency of theintermediate frequency signal to be selected according to a frequencyband of the IF filter that is adjusted according to the frequency bandof the intermediate frequency signal.
 9. The frequency signal receivingdevice according to claim 8, wherein the second memory part is equippedwith a plurality of second registers equipped with the secondinformation set for each frequency band of the intermediate frequencysignal that is assumed in advance; and a center frequency of the localoscillation frequency signal is adjusted on the basis of the secondinformation of the second register selected according to a frequencyband of the intermediate frequency inputted.
 10. The signal receivingdevice according to claim 5, wherein the condenser block in thehigh-pass filter comprises: an inputting terminal to receive theintermediate frequency signal; a connecting terminal to connect to thelow-pass filter; and a plurality of condensers connected in parallel toeach other between the inputting terminal and the connecting terminalvia a corresponding switch respectively, and the switch is turned on oroff based on a content of a first control input.
 11. The signalreceiving device according to claim 5 wherein the condenser block in thelow-pass filter comprises: a connecting terminal to connect to thehigh-pass filter; an outputting terminal to output the predeterminedband signal; and a plurality of condensers connected in parallel to eachother between the connecting terminal and the outputting terminal via acorresponding switch respectively, and the switch is turned on or off onthe basis of a content of the first control input.
 12. A frequencysignal receiving method characterized in that it comprises: a mixer stepto mix a frequency signal received with a local oscillation frequencysignal generated by a local oscillator so as to generate an intermediatefrequency signal; a filter step to pass a predetermined frequencycomponent of the intermediate frequency signal by an IF filter in whicha center frequency of a passable frequency signal and a frequency bandare set; a first adjusting step to adjust a frequency band set in the IFfilter according to the frequency band of the intermediate frequencysignal; a second adjusting step to adjust a center frequency of theintermediate frequency signal according to a fluctuation of the centerfrequency set in the IF filter caused by adjustment of a frequency bandset in the IF filter; and a demodulating step to demodulate theintermediate frequency signal that has passed through the IF filter. 13.The frequency signal receiving method according to claim 12 wherein acenter frequency of the intermediate frequency signal is adjusted byadjusting a center frequency of the local oscillation frequency signaloutputted from the local oscillator.
 14. The frequency signal receivingmethod according to claim 13 wherein a frequency band set in the IFfilter is adjusted based on first information on a frequency band of theIF filter set for each frequency band of the intermediate frequencysignal that is assumed in advance.
 15. The frequency signal receivingmethod according to claim 12 wherein a center frequency of the localoscillation frequency signal is adjusted based on second information ona center frequency of the local oscillation frequency signal set foreach frequency band of the intermediate frequency signal that is assumedin advance.
 16. The frequency signal receiving device according to claim1 wherein the IF filter comprises a capacity element and a resistanceblock that is connected to the capacity element and a resistance valueis switchable; and a frequency band set in the IF filter is adjusted byadjusting a resistance value of the resistance block.